Step 2 There are two things you need to know about the screw guns prior to using them. First, each gun has a battery in the base of the grip. Once the battery starts to run low, you can replace it by depressing the two tabs on either side of the battery, slide the battery out, then insert a charged one.     MAKE SURE TO PLACE DISCHARGED BATTERIES IN THE APPROPRIATE CHARGERS!!! Second, each gun can run in forward or reverse. Although the switch varies from gun to gun, most are found just above the trigger.